A tooth is an organ having enamel in the outermost layer and dentin in its inner layer, both of which are hard tissues; an odontoblast, which produces the dentin, inside the dentin; and dental pulp in the central portion. Teeth may be lost by dental caries, periodontal diseases or the like, and from the viewpoint of the significant influence of the presence or absence of teeth on appearance and taste of food, and from the viewpoint of maintaining health and a high quality of life, various tooth regenerative techniques have been developed.
For example, in J. Dent. Res., 2002, Vol. 81(10), pp. 695-700, it is disclosed that a tooth-like tissue is regenerated by transplanting cells, such as epithelial cells isolated from a tooth germ and mesenchymal dental follicle cells, with a biodegradative carrier into an abdominal cavity of a rat.
As a method of regenerating a tooth germ, it is described, for example, in Japanese Patent Application Laid-open (JP-A) No. 2004-331557, that tooth germ cells isolated from a living body are cultured in the presence of biologically active substances such as fibroblast growth factors and the like. In JP-A No. 2004-357567, it is proposed that at least one type of cells selected from tooth germ cells and cells which can be differentiated into these tooth germ cells, both of them are isolated from a living body, are cultured along with a fibrin-containing carrier, and it is described that a “tooth” having a specific shape is formed by using a fibrin-containing carrier having the desired shape for the tooth germ.
On the other hand, from the viewpoint of regenerative medicine, recent interest has focused on reuse of biological samples which had been hitherto discarded. Especially, unlike tissues excised due to diseases, recent interest has focused on tissues such as umbilical cord and amnion, which had been discarded at delivery, as organs having stem cells and capable of being involved in cell differentiation.
Examples of the techniques which focus attention on amnion include JP-A 2006-6249 which discloses a technique in which epithelial cells and interstitial cells derived from amnion are grown in a large amount in an undifferentiated state. It describes that cells grown by this method are useful in regenerative medicine and the like since they have multipotency similar to that of undifferentiated embryonic stem cells.
JP A 2004-254682 describes that side population cells were isolated from the human amniotic mesenchymal cell layer and human amniotic epithelial cell layer as stem cells. It describes that the side population cells are at least capable of differentiating into nerve cells and useful as the source of substances produced by nerve cells.